Brake problems have been discussed to death on this board. Now it is my turn.

I have a 1965 Valiant that was long ago converted to a dual brake system. You might think that this would be a good thing, but for some reason it isn't.

That's because you have to use clown feet levels of pressure on the pedal to get it to stop. I don't believe it is possible to "lock 'em up." This is not a good car for people prone to tailgating. You can get it stopped, but stops are best planned for.

Compare this mess to the stopping power of one of my other Valiants, old Veronica, a 1963 V-200 4-door sedan grocery getter, that is nearly stone stock and sports a "Death Onion" in all of its glory. That old girl can stop on a dime and her stock brakes are strong enough that I even trust her to tow a small trailer.

So lets discuss equipment. At the wheels, the `65 has stock drum brakes fore and aft. Over the course of the forever that I have had this car, I have replaced everything in the braking system at least once. Most recent attempts at better brakes include new drums, new hoses, and *brand new* metal lines up front. The shoes are recent, as are the wheel cylinders. The master cylinder is fairly new. All of this, and it still feels like I have brakes from a go-cart on it. Meanwhile, the single piston system on old Veronica mocks my efforts with 5 times the stopping power. I am tempted to just put a stock system back in the `65 and keep it well maintained like I do the `63.

So what am I missing? The fluid seems to be flowing just fine when I bleed the system, so I'm pretty confident the system is not restricted in any way. The brakes don't seem to be pulling, they are just require Big Foot to apply them.

Its a puzzle. Thanks in advance for your suggestions.

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1961, 1962, 1963 and 1965 Valiant 200. The `65 is a `vert.

What's the bore size of the dual master vs the single master?

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Try 1" bore master cylinder.

I have looked all over my electronic and paper records for some indication of what I have on the car now, but evidently it got lost in the shuffle.

According to the shop manual, the single chamber M/C has a 1" bore. How can I determine the bore of the M/C I have on the car now? If I need to replace the M/C, which dual chamber M/C has a 1" bore?

Thanks for your continued help.

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1961, 1962, 1963 and 1965 Valiant 200. The `65 is a `vert.

If you bought a manual brake master cylinder for a '71 and later A-body (whether disc or drum type), then you probably got one with a bore of 1-1/32". With the caveat that a lot of application listings are flat-out wrong.

If you want a dual reservoir master with a 1" bore, try ordering one for a 67-70 Valiant/Dart. RockAuto usually has at least some with the bore diameter specifically listed if you want to be sure. FYI, the front disc master cylinders have a much larger rear reservoir (for the front circuit). In this era (pre-'73, I think?) there may or may not be differences in built-in residual pressure valves between disc and drum masters.

All that being said, I'm not sure the difference you describe between your two cars (both 4-wheel drum, I assume) can be blamed entirely on a 1/32" difference in bore diameter (~6% increase in area). I have a 1-1/32" master cylinder on a '64 Dart sedan and a '64 Valiant wagon both with 9" drum brakes, and the pedal effort on those isn't as bad as what you're describing. What kind of brake shoes are you using?

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

Yes, I would look at brake shoe type/material. That much difference in bore will not produce the difference you are describing.

Lou

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Home of Slant6-powered fun machines

Tell us about the timing of those sentences… when you first converted to dual master, what else did you change at the same time? And did the Big Foot problem happen immediately?

Your symptoms mirror exactly what I find with 9" drum brakes after they've gotten toasty warm after a panic stop or a long downgrade. That makes me think the friction surfaces are a likely contributor. In the extremely unlikely scenario that you've got them adjusted so tight that the car barely rolls, and the shoes are always warm, then the solution is obvious. (If it behaves differently when stone cold than after driving, that might be worth investigating further.)

But since it would be difficult to imagine that you hadn't thought of that, the next logical suggestion is soiled or contaminated shoe linings. A dab of grease somewhere? Or something that soaked into the shoes during storage and is slowly making its way to the surface as it goes through normal heat and usage cycles?

For sure, it's not normal, and it's not a side effect of simply going from single to dual masters. When I replaced the single pot master (1964) with a dual (1967 or 68 from NAPA as I recall), there was virtually no difference in feel. So it can be done.

A pressure gauge in either front or rear lines might be an interesting diagnostic.

- Erik

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Lots of early Valiants and Barracudas have crossed my path.
Also a handful of other toys for variety now and then.

agree with getting a brake pressure gauge

https://www.amazon.com/SSBC-A1704-Brake ... B003VYVFSS

and compare pressures at the wheel cylinders between the vehicles.
that will tell you if it is a system ( brake master cylinder or distribution block) or a brake component (shoes - drums) issue.

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Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

Something fishy about that Amazon link. Why would a gauge need 3000 psi? That's about double what I'd expect. And the reviews don't look promising, either. I know SSBC is famous for aftermarket brakes, but… really?

A quick search to confirm my pressure recollections yielded this article. I have no affiliation nor know anything about the company that wrote it, but given that they specialize in building brakes for race cars, and sell a few products that seem quite a bit more high-end than the average Chinesium product through Amazon, the overall smell is better than what Amazon provided. For about the same price! If you buy either, let us know what you think.

- Erik

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Lots of early Valiants and Barracudas have crossed my path.

Also a handful of other toys for variety now and then.

Holy cow: as I researched SSBC's reputation, I discovered this fascinating link which describes a similar pressure problem, and quite clearly implicates a proportioning valve. I'm struck by the brilliance.

- Erik

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Lots of early Valiants and Barracudas have crossed my path.

Also a handful of other toys for variety now and then.

The link is just an example of a brake pressure gauge,
for the benefit of the guy with the braking issue.
Not an endorsement.
I did not think that I should need to say that.

Since you asked, typically gauges are most accurate towards the middle of their scale and
less accurate at the lowest and highest ranges.
So if one was measuring peak hydraulic brake pressures with expected values of 1000 to 1500 psi.
a 3000 psi max gauge could be appropriate.

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Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

Yes, and add to that your average counter man who has never heard of a Valiant, much less a modified one,
and trouble is bound to follow.



So it is entirely possible that I have the wrong M/C on my car. That bit about the larger rear reservoir.
The M/C I have now has a much larger rear reservoir, perhaps double the size.
I just looked up a M/C for a 68 Valiant and it looks much different from the one I have.
What I have now bears more than a passing resemblance to the M/C I have in my 62 Valiant,
which has a disk brake system from a 74 Dart in it. This incredibly long link is what I am looking at right now:

https://www.rockauto.com/en/moreinfo.php?pk=309048&cc=1242795&jsn=398&_nck=ZExt1ysfqhqWnq%2BEvUNdS3Txyey60IDtnjPWF5UU9J0BWQv7pvqZbkEUk86%2BAYIh8MwADrWeNyZF%2FkN8k9%2B9aAxLK%2Bnil9xrvQquvSCIPFasN27aR1%2BKk8bMEoYuT%2BL%2BQQjwJWZXTItavqA%2BOnRe%2F2I7dXDTEYGiOEi569bTLhdF3C9R5ZkBkWYUnBhlJBy%2FvX94T%2FNON7cerbkq4TdxARUUkG%2BlC3L%2FGinLwB6nBkn3ywbaYCSad%2FazRoIIW%2B8WWlPDVOiHvPVcsrbrhB04%2FFz8PmWqo5CDg0yhkwqdkMrH9E6GYoITMWXS7CQvQFieveNZLxae4HVPqg7vFwt7ncsLKmKZ34soKQDoSSyl1YBQmV8coxzsgvA8vGRTxUf4



I try to buy name brands from Rock Auto. I have replaced the shoes many times, but nothing seems to help.
The brakes are always at best marginal and at worst terrifying. They are closer to the terrifying end of the spectrum right now.
By the way, my first Valiant was a 64 V-200 station wagon that I drove in high school.

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1961, 1962, 1963 and 1965 Valiant 200. The `65 is a `vert.

Amen to that.

Any proportioning valve in the system? If so, don't miss my previous post. Pure brilliance.

A hydraulic pressure test is making more and more useful, if only because it seems you've already tried everything else.

- Erik

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Lots of early Valiants and Barracudas have crossed my path.

Also a handful of other toys for variety now and then.

I first converted the car to a dual system in the late 80's. At that time I replaced the M/C, the proportioning valve and most of the metal lines. It has not always been this bad. It worked acceptably for several years, always with the usual problem of the occasional leaking wheel cylinder. I think it got worse when I had to replace the M/C but, to be clear, the brakes in the 65 have never been as good as stock.



I agree that the symptoms are similar to brake fade, and the friction surfaces are definitely suspect, but they are not adjusted to the point of dragging. Here's the thing though, these are not the only shoes that have given me poor stopping power. Over the years I have changed the shoes countless times and the drums a few times as well.



A valid question. I will pop the drums off and take a look. But if they are contaminated they must be contaminated on both sides equally because there is no pulling to one side when braking.



I will look into that. Thanks for your thoughts, Erik

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1961, 1962, 1963 and 1965 Valiant 200. The `65 is a `vert.

I did a little poking around of my own and came up with this 10 year old discussion about Master Cylinders:

http://www.slantsix.org/forum/viewtopic.php?t=33250

In it, Slant Six Dan suggests using a Raybestos MC36338, with a 15/16" bore. I looked up this part and, once again, it looks vastly different than the one I have in my car now. Does this sound like a good option for me? Have any of you used an MC36338 in your car?

Thanks for hanging in with me on this.

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1961, 1962, 1963 and 1965 Valiant 200. The `65 is a `vert.